Genetics The study of heredity

GeneticsThe study of heredity

• Genes are found on chromosomes. Chromosomes are made up of DNA.

Alleles: Different forms of a gene.

Dominant: If the dominant allele (gene) is present, the organism will show that trait.Recessive: Trait will be exhibited only if organism does not have dominant allele or is pure for recessive trait.

Gregor Mendel (1822-1884)An Austrian monk who cultivated and studied garden pea plants. His studies produced the basic concepts of heredity.

Trait Dominant Allele

Recessive Allele

PossibleGenotype

PossiblePhenotyp

esSeed Color

G (green) g (yellow)

GGHomozygous

GgHeterozygous

gg

Green

Green

YellowFlower Color

P (purple) p (white) PPHomozygous

PpHeterozygous

pp

Purple

Purple

white

Genotype: The Allele combination, heterozygous (hybrid) or homozygous (gg, GG, or Gg).Phenotype: The physical characteristic displayed (green or yellow).

Why Pea Plants?

•Many observable contrasting traits.

•Easy to grow.

•Short time between one generation and the next.

Structure of flower

Cross Pollination

Punnett Square In Pea plants Green pods (G) are dominant over yellow (g)

pods.

Genotype PhenotypeGG homozygous Green PodGg heterozygous Green Podgg Yellow Pod P Cross : GG x gg Possible Gametes : ____ ____ X ____ ____

GgGreen Pod

GgGreen Pod

GgGreen Pod

GgGreen Pod

F1 Genotypic ratio:

F1 Phenotypic ratio:

g g

G

G

F1 Cross: Gg x Gg Possible Gametes: ____ ____ X ____ ____

F2 Genotypic ratio:

F2 Phenotypic ratio:

In mice black is dominant over white; B – black, b- white, BB homozygous black, Bb

heterozygous black, bb recessive whiteCross two heterozygous black mice, Bb x Bb

Cross : Bb x Bb Possible Gametes : ____ ____ X ____ ____

Genotypic ratio:

Phenotypic ratio:

Test Cross

Is this back mouse homozygous black BB or heterozygous black Bb?

One way to find out is to do a Test Cross. Cross this black mouse with the recessive white bb.

BB x bb Bb x bb

If any of the offspring produced are white or show the recessive trait, then the black mouse had to be heterozygous Bb.

If all of the offspring produced are black, you cannot be 100% positive that the black mouse is homozygous BB because the

inheritance of a an allele is a 50/50 chance.

Monohybrid Cross: Rr x Rr

Dihybrid Cross: RrYy x RrYy

Dihybrid Cross

P Cross: TTRR ( pure tall & round) x ttrr (pure short & wrikled) _____ _____ ______ _____ _____ _____ _____ _____

2 traits; plant height and seed color

F1 Cross TtRr (hybrid tall & round) x TtRr (hybrid tall & round)

_____ _____ _____ _____ _____ _____ _____ _____

F2 Genotype F2 Phenotype

Incomplete Dominance

RWPink

RWPink

RWPink

RWPink

W WR

R

GenotypePhenotypeRR Red flowerWW White flower RW Pink flowerP Cross: RR x WW

F1 Genotype: 100% RW

F1 Phenotype: 100% Pink flower

Co dominance

RWRoan

RWRoan

RWRoan

RWRoan

W WR R

Genotype PhenotypeRR Red cowWW White cowRW Roan cow

P Cross: RR x WW

Genotype of F1 offspring: 100% RW

Phenotype of F1 offspring: 100% Roan

Multiple AllelesBlood Types

Allele Antigen on RBC IA A IB B i none

Genotype PhenotypeIA IA homozygous Type AIA i heterozygous Type AIB IB homozygous Type BIB i heterozygous Type BIA IB Type ABi i Type O

Crosses Involving Multiple Alleles

Cross: a man who is homozygousfor blood type A with a womanwho is homozygous blood type B.

IA IA x IB IB

Cross: a man who is heterozygousfor blood type A with a womanwho is blood type O. IA i x i i

IA IB

Type AB

IA IB

Type AB

IA IB

Type AB

IA IB

Type AB

IA iType A

IA iType A

i iType O

i iType O

IB IB

IA

IA

i i

IA

i

Sex Determination

Sex Linked Traits Traits located on the X chromosome

Genotype PhenotypeXX Normal FemaleXcXCarrier FemaleXcXc Colorblind FemaleXY Normal MaleXcYColorblind Male

Cross: A normal male with a carrier female. XY x XcX

Xc XCarrier Female

XcYColorblind

Male

XXNormal Female

XYNormal Male

X Y

Xc

X

Cross: A colorblind male with a carrier female. XcY x XcX

Xc XcColorblind

Female

Xc YColorblind

male

Xc XCarrier Female

X YNormal Male

Xc Y

Xc

X

Human Pedigree Key

Human Pedigree Autosomal Recessive

Human Pedigree Autosomal Dominant

Human Pedigree Sex linked Recessive

http://www.zerobio.com/drag_gr11/pedigree/pedigree4.htm

Chromosomes

Karyotype

Female XX Male XY